kvm: x86: vmx: NULL out hwapic_isr_update() in case of !enable_apicv

In most cases calling hwapic_isr_update(), we always check if
kvm_apic_vid_enabled() == 1, but actually,
kvm_apic_vid_enabled()
    -> kvm_x86_ops->vm_has_apicv()
        -> vmx_vm_has_apicv() or '0' in svm case
            -> return enable_apicv && irqchip_in_kernel(kvm)

So its a little cost to recall vmx_vm_has_apicv() inside
hwapic_isr_update(), here just NULL out hwapic_isr_update() in
case of !enable_apicv inside hardware_setup() then make all
related stuffs follow this. Note we don't check this under that
condition of irqchip_in_kernel() since we should make sure
definitely any caller don't work  without in-kernel irqchip.
Signed-off-by: Tiejun Chen <tiejun.chen@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/lapic.c

@@ -402,7 +402,7 @@ static inline void apic_set_isr(int vec, struct kvm_lapic *apic)
 	 * because the processor can modify ISR under the hood.  Instead
 	 * just set SVI.
 	 */
-	if (unlikely(kvm_apic_vid_enabled(vcpu->kvm)))
+	if (unlikely(kvm_x86_ops->hwapic_isr_update))
 		kvm_x86_ops->hwapic_isr_update(vcpu->kvm, vec);
 	else {
 		++apic->isr_count;
@@ -450,7 +450,7 @@ static inline void apic_clear_isr(int vec, struct kvm_lapic *apic)
 	 * on the other hand isr_count and highest_isr_cache are unused
 	 * and must be left alone.
 	 */
-	if (unlikely(kvm_apic_vid_enabled(vcpu->kvm)))
+	if (unlikely(kvm_x86_ops->hwapic_isr_update))
 		kvm_x86_ops->hwapic_isr_update(vcpu->kvm,
 					       apic_find_highest_isr(apic));
 	else {
@@ -1742,7 +1742,9 @@ void kvm_apic_post_state_restore(struct kvm_vcpu *vcpu,
 	if (kvm_x86_ops->hwapic_irr_update)
 		kvm_x86_ops->hwapic_irr_update(vcpu,
 				apic_find_highest_irr(apic));
-	kvm_x86_ops->hwapic_isr_update(vcpu->kvm, apic_find_highest_isr(apic));
+	if (unlikely(kvm_x86_ops->hwapic_isr_update))
+		kvm_x86_ops->hwapic_isr_update(vcpu->kvm,
+				apic_find_highest_isr(apic));
 	kvm_make_request(KVM_REQ_EVENT, vcpu);
 	kvm_rtc_eoi_tracking_restore_one(vcpu);
 }

arch/x86/kvm/vmx.c

@@ -5895,6 +5895,7 @@ static __init int hardware_setup(void)
 		kvm_x86_ops->update_cr8_intercept = NULL;
 	else {
 		kvm_x86_ops->hwapic_irr_update = NULL;
+		kvm_x86_ops->hwapic_isr_update = NULL;
 		kvm_x86_ops->deliver_posted_interrupt = NULL;
 		kvm_x86_ops->sync_pir_to_irr = vmx_sync_pir_to_irr_dummy;
 	}
@@ -7478,9 +7479,6 @@ static void vmx_hwapic_isr_update(struct kvm *kvm, int isr)
 	u16 status;
 	u8 old;
 
-	if (!vmx_vm_has_apicv(kvm))
-		return;
-
 	if (isr == -1)
 		isr = 0;